U.S. patent application number 13/822522 was filed with the patent office on 2013-08-01 for idca for fast cooldown and extended operating time.
This patent application is currently assigned to LOCKHEED MARTIN CORPORATION. The applicant listed for this patent is Vincent Loung, Elna Saito, Jeff W. Scott. Invention is credited to Vincent Loung, Elna Saito, Jeff W. Scott.
Application Number | 20130192275 13/822522 |
Document ID | / |
Family ID | 47601477 |
Filed Date | 2013-08-01 |
United States Patent
Application |
20130192275 |
Kind Code |
A1 |
Loung; Vincent ; et
al. |
August 1, 2013 |
IDCA FOR FAST COOLDOWN AND EXTENDED OPERATING TIME
Abstract
Systems, methods, and devices for integrated detector cooler
assemblies (IDCAs) and multi-circuit cryostats are discussed
herein. Solutions include using cryostats with multiple cooling
circuits. Some cryostat variations may include a rapid cooldown
circuit and a temperature maintenance circuit. In some cases, the
temperature maintenance circuit may be a closed-loop circuit run by
a compressor instead of an open-loop circuit run on a pressurized
gas bottle/cartridge. Variations of a cryostat may also include a
gas expander portion that replaces the coldfinger of typical IDCAs.
Further variations of cooling circuits may include circuits that
perform reverse-flow heat exchange to pre-cool incoming refrigerant
and also cooling circuits that have heat bridges disposed thereon
to assist in such heat exchange.
Inventors: |
Loung; Vincent; (Lompoc,
CA) ; Saito; Elna; (Santa Barbara, CA) ;
Scott; Jeff W.; (Santa Barbara, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Loung; Vincent
Saito; Elna
Scott; Jeff W. |
Lompoc
Santa Barbara
Santa Barbara |
CA
CA
CA |
US
US
US |
|
|
Assignee: |
LOCKHEED MARTIN CORPORATION
Bethesda
MD
|
Family ID: |
47601477 |
Appl. No.: |
13/822522 |
Filed: |
July 20, 2012 |
PCT Filed: |
July 20, 2012 |
PCT NO: |
PCT/US2012/047688 |
371 Date: |
March 12, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61510903 |
Jul 22, 2011 |
|
|
|
61530312 |
Sep 1, 2011 |
|
|
|
Current U.S.
Class: |
62/51.1 |
Current CPC
Class: |
H05K 7/20372 20130101;
H05K 7/20254 20130101; F25B 9/02 20130101; F25B 39/02 20130101;
F25B 19/02 20130101; F25B 2339/02 20130101; H05K 7/20354
20130101 |
Class at
Publication: |
62/51.1 |
International
Class: |
F25B 9/02 20060101
F25B009/02 |
Claims
1. An integrated detector cooler assembly (IDCA) comprising: a
cryostat having at least two cooling circuits disposed therein; and
a first refrigerant source having a mixed-gas refrigerant to be
provided to at least one of said cooling circuits; where a first of
said cooling circuits is operable in a high-flow, rapid cooling
mode; and a second of said cooling circuits is operable in
low-flow, temperature maintenance mode.
2. The IDCA of claim 1, the IDCA further comprising a compressor;
and where the first refrigerant source provides refrigerant to the
first cooling circuit, said first cooling circuit being configured
for open-loop operation; and where the compressor provides
refrigerant to the second cooling circuit, said second cooling
circuit being configured for closed-loop operation.
3. The IDCA of claim 1, the IDCA further comprising a second
refrigerant source; and where the first refrigerant source provides
refrigerant to the first cooling circuit, said first cooling
circuit being configured for open-loop operation; and where the
second refrigerant source provides refrigerant to the second
cooling circuit, said second cooling circuit being configured for
open-loop operation.
4. The IDCA of claim 1, where at least one cooling circuit is
equipped with a gas expander portion, and where the gas expander
portion is disposed in a center of the cryostat.
5. (canceled)
6. The IDCA of claim 1, where at least one cooling circuit is
configured to operate as a reverse-flow heat exchanger, such that
refrigerant entering the cooling circuit is cooled by refrigerant
leaving the circuit.
7. The IDCA of claim 1, where at least one cooling circuit includes
heat-transfer bridges disposed on the cryostat along said cooling
circuit to transfer heat between high-pressure and low-pressure
portions of the cooling circuit, where the high-pressure portion of
the cooling circuit is associated with refrigerant flowing into the
circuit and the low-pressure portion of the cooling circuit is
associated with refrigerant flowing out of the circuit.
8. The IDCA of claim 1, the IDCA further comprising a control
portion; and where the control portion controls operation of the
first and second circuits by activating the first circuit to bring
a photodetector disposed on the cryostat to a desired operating
temperature; activating the second circuit to maintain the
photodetector at the desired operating temperature.
9. The IDCA of claim 1, the IDCA further comprising a switching
portion that controls a flow of refrigerant from the refrigerant
source to at least one of the cooling circuits.
10. The IDCA of claim 1, the IDCA further comprising: a first
switching portion that controls a flow of refrigerant from the
first refrigerant source to the first cooling circuit; and a second
switching portion that controls a flow of refrigerant to the second
cooling circuit.
11. The IDCA of claim 7, where: the first and second cooling
circuits are both equipped with said heat transfer bridges; the
first and second cooling circuits are both equipped with gas
expander portions disposed at a center of the cryostat; the
cryostat a planar, disk-shaped Joule-Thomson cryostat; the first
cooling circuit is disposed on a first half of the disk; and the
second cooling circuit is disposed on a second half of the
disk.
12. The IDCA of claim 6, where: the first and second cooling
circuits are both configured to operate as reverse-flow heat
exchangers; the first and second cooling circuits are both equipped
with gas expander portions disposed at a center of the cryostat;
the cryostat a planar, disk-shaped Joule-Thomson cryostat; the
first cooling circuit is disposed on a first half of the disk; and
the second cooling circuit is disposed on a second half of the
disk.
13. The IDCA of claim 4, where the gas expander portion is the
coldest portion of the cryostat, and where an FPA disposed in the
IDCA is positioned above the gas expander portion of the cryostat
such that the gas expander portion is in thermal contact with the
FPA.
14. The IDCA of claim 1, the IDCA further comprising a high
operating temperature (HOT) infra-red (IR) photodetector disposed
on the cryostat.
15. The IDCA of claim 1, where the mixed-gas refrigerant includes
one or more of ethane, methane, or isobutane.
16. The IDCA of claim 1, where the first refrigerant source
supplies the refrigerant used to operate the second cooling
circuit.
17. The IDCA of claim 16, where the refrigerant used to operate the
second cooling circuit is recovered from a refrigerant exhaust of
the first cooling circuit.
18-26. (canceled)
27. A method of cooling a focal plane array (FPA) disposed in an
integrated detector cooler assembly (IDCA) to an operating
temperature, the method comprising: executing a rapid cooldown
process to bring the FPA down to a desired operating temperature;
and executing a temperature maintenance process to maintain the FPA
at the desired operating temperature, where the temperature
maintenance process includes providing a pressurized gas
refrigerant to a low-flow cooling circuit included in a planar,
disk-shaped Joule-Thomson cryostat included in the IDCA.
28. The method of claim 27, where the low-flow cooling circuit is a
closed loop cooling circuit and where the pressurized gas
refrigerant provided to the low-flow cooling circuit is provided by
a compressor included in the IDCA.
29. A method of cooling a focal plane array (FPA) disposed in an
integrated detector cooler assembly (IDCA) to an operating
temperature, the method comprising: executing a rapid cooldown
process to bring the FPA down to a desired operating temperature;
executing a temperature maintenance process to maintain the FPA at
the desired operating temperature; determining whether the FPA is
at the desired operating temperature; performing said rapid
cooldown process in response to a determination that the FPA is not
at the desired operating temperature; and performing said
temperature maintenance process in response to a determination that
the FPA is at the desired operating temperature.
30-31. (canceled)
32. The method of claim 27, the method further comprising receiving
an activation signal directing the FPA to begin imaging, where said
determining is performed in response to receiving said activation
signal.
33. A planar, disk-shaped J-T cryostat, the cryostat comprising: a
cooling circuit configured to operate as a reverse-flow heat
exchanger such that refrigerant entering the circuit via a
refrigerant inlet port is cooled by refrigerant leaving the circuit
via a refrigerant outlet port; a refrigerant source providing a
mixed-gas refrigerant to said cooling circuit; and heat transfer
bridges disposed on said the cryostat along said cooling circuit,
said heat transfer bridges being configured to enhance the
reverse-flow heat exchange operation of the cooling circuit.
34. (canceled)
35. The cryostat of claim 33, where the heat transfer bridges
include polysilicon.
36. The cryostat of claim 33, where the heat transfer bridges have
a coefficient of thermal expansion (CTE) that matches the CTE of
the cryostat.
37. The cryostat of claim 33, the cryostat further comprising a
second cooling circuit configured to operate as a reverse-flow heat
exchange, where the heat transfer bridges are disposed on the
cryostat along said first and second cooling circuits.
38. The cryostat of claim 33, where: the cryostat is formed from
two glass plates, an upper plate and a lower plate; where the
cooling circuit is etched into the lower plate; where the upper
plate includes heat transfer bridge pockets to accommodate said
heat transfer bridges therein; and where the upper and lower plates
are bonded together to form the cryostat.
Description
PRIORITY
[0001] This non-provisional application claims priority under 35
U.S.C. .sctn.119(e) to U.S. Provisional Application No. 61/510,903
filed on Jul. 22, 2011, and U.S. Provisional Application No.
61/530,312 filed on Sep. 1, 2011, the entire contents of which are
hereby incorporated by reference.
BACKGROUND
[0002] For some IR sensor applications, it is generally not
possible to meet two critical performance requirements with the
same system design configuration: very fast cooldown time (seconds
to reach Sensor operating temperature) and long system operational
run times (enabling the system to operate for thousands of hours
without maintenance or service). In some cases, the ability to
abort a mission and re-use the device at a later date can be a
desirable feature and adds operational flexibility. This is not
possible with current technology.
[0003] The requirements for achieving very quick cooldown time to
operating temperature and maintaining long operational run times
are considered mutually exclusive for applications where weight,
size and power are a premium. Applications such as a seeker on a
missile or a surveillance sensor, generally need to be small,
lightweight, portable and adaptable. So there is generally a
trade-off between quick cooldown time and operational run time
because of size and weight constrains.
[0004] Cryocoolers designed for applications requiring very fast
turn on times are generally based on the Joule Thomson (J-T) effect
because of the very high rates of cooling achievable with this
cooling cycle. As a result, missile applications typically use
conventional J-T cooling approaches because fast cooldown times are
crucial to the program. However, J-T type coolers suffer from
relatively short run times because of the size, weight and power
penalty associated with running these coolers for long periods of
time. J-T cryostats can be made very small, lightweight and compact
but lack operational run time. To achieve very long operational run
times, these coolers require either large reservoir volumes of very
high pressure gasses or very large compressors to supply very high
pressure gasses. Both solutions add to the size weight and power to
the device.
[0005] Applications which require long run times are met with other
types of coolers. These cryocoolers are generally Stirling and
pulse-tube based and meet the long continuous operation
requirements. They are small in size, light weight and have very
high efficiencies. However, they cannot match the high cooling
rates of J-T coolers and therefore suffer from longer cooldown
times when compared to J-T cryostats. Making such Stirling and
pulse-tube cryocooler systems have shorter cool-down times also
adds bulk and power. Either solution results in very large, heavy
and bulky systems.
[0006] Furthermore, the future trend in sensor technology is to
employ larger sensors packaged in smaller spaces, light weight and
requiring very low power to operate. In addition, these sensors
have to be cooled reliably to operating temperatures and meet a
host of other specific performance requirements such as the time
the sensor requires to get to its operating temperature, the
efficiency of the process, minimum input power to maintain
temperature, the size and weight of the system, the operating time
for a mission and the operating life of a system. Currently, the
type of coolers used to achieve these performance requirements are
large and are not easily adaptable to meeting diverse requirements
because they were designed purely and solely for achieving
cryogenic temperatures.
SUMMARY
[0007] Aspects of the techniques and solutions disclosed herein are
directed at solving the above-noted problems of FPA cooling, IDCA
size, power consumption, and operating times.
[0008] Variations of systems and solutions discussed herein may
pertain to an integrated detector cooler assembly (IDCA)
comprising: a cryostat having at least two cooling circuits
disposed therein; and a first refrigerant source having a mixed-gas
refrigerant to be provided to at least one of said cooling
circuits; where a first of said cooling circuits is operable in a
high-flow, rapid cooling mode; and a second of said cooling
circuits is operable in low-flow, temperature maintenance mode.
[0009] In some variations, the IDCA may further include a
compressor and be configured such that the first refrigerant source
provides refrigerant to the first cooling circuit, said first
cooling circuit being configured for open-loop operation; and the
compressor provides refrigerant to the second cooling circuit, said
second cooling circuit being configured for closed-loop
operation.
[0010] In some variations, the IDCA may include a second
refrigerant source and be configured such that the first
refrigerant source provides refrigerant to the first cooling
circuit, said first cooling circuit being configured for open-loop
operation; and the second refrigerant source provides refrigerant
to the second cooling circuit, said second cooling circuit being
configured for open-loop operation.
[0011] In some variations, at least one cooling circuit is equipped
with a gas expander portion, and where the gas expander portion is
disposed in a center of the cryostat. In some variations, the
cryostat is a planar, disk-shaped, Joule-Thomson (JT) cryostat. In
yet further variations, the gas expander portion is the coldest
portion of the cryostat, and an FPA disposed in the IDCA is
positioned above the gas expander portion of the cryostat.
[0012] In further variations, at least one cooling circuit is
configured to operate as a reverse-flow or counter-current heat
exchanger, such that refrigerant entering the cooling circuit is
cooled by refrigerant leaving the circuit. In some variations, the
reverse-flow or counter-current heat exchanger may operate based on
the principles demonstrated in U.S. Pat. No. 5,644,502, issued to
Little on Jul. 1, 1997, the entire contents of which are hereby
incorporated by reference.
[0013] In some variations, at least one cooling circuit includes
heat-transfer bridges to transfer heat between high-pressure and
low-pressure portions of the cooling circuit, where the
high-pressure portion of the cooling circuit is associated with
refrigerant flowing into the circuit and the low-pressure portion
of the cooling circuit is associated with refrigerant flowing out
of the circuit.
[0014] In some variations, the IDCA includes a control portion that
controls operation of the first and second circuits by activating
the first circuit to bring the photodetector to a desired operating
temperature; and activating the second circuit to maintain the
photodetector at the desired operating temperature.
[0015] In some variations, the IDCA includes a switching portion
that controls a flow of refrigerant from the refrigerant source to
at least one of the cooling circuits. In further variations, the
IDCA includes a first switching portion that controls a flow of
refrigerant from the first refrigerant source to the first cooling
circuit; and a second switching portion that controls a flow of
refrigerant to the second cooling circuit.
[0016] In some variations, the first and second cooling circuits
are both equipped with said heat transfer bridges; the first and
second cooling circuits are both equipped with gas expander
portions disposed at a center of the cryostat; the cryostat a
planar, disk-shaped Joule-Thomson cryostat; the first cooling
circuit is disposed on a first half of the disk; and the second
cooling circuit is disposed on a second half of the disk.
[0017] In other variations, the first and second cooling circuits
are both configured to operate as reverse-flow heat exchangers. In
some such variations, the first and second cooling circuits are
both equipped with gas expander portions disposed at a center of
the cryostat; the cryostat a planar, disk-shaped Joule-Thomson
cryostat; the first cooling circuit is disposed on a first half of
the disk; and the second cooling circuit is disposed on a second
half of the disk.
[0018] Variations of systems and solutions discussed herein may
pertain to a planar, disk-shaped J-T cryostat, the cryostat
comprising: a first cooling circuit operable in a low-flow,
temperature maintenance mode; a second cooling circuit operable in
an high-flow, fast cooling mode; and a first refrigerant source
providing a mixed-gas refrigerant to at least one of said cooling
circuits; where the first and second cooling circuits are each
equipped with a refrigerant inlet port and a refrigerant outlet
port; and where the first and second cooling circuits are each
configured to operate as reverse-flow heat exchangers such that
refrigerant entering the circuit via the refrigerant inlet port is
cooled by refrigerant leaving the circuit via the refrigerant
outlet port.
[0019] In some variations, at least one cooling circuit is equipped
with a gas expander portion disposed in a center of the cryostat,
the gas expander portion being configured to receive high-pressure
refrigerant via the refrigerant inlet port and direct low-pressure
refrigerant to the refrigerant outlet port, such that the gas
expander portion is the coldest portion of the cooling circuit. In
further variations, each cooling circuit is equipped with the gas
expander portion. In further variations, the second cooling circuit
is configured to operate in an open loop mode and the first cooling
circuit is configured to operate in a closed loop mode.
[0020] In some variations, the cryostat includes heat transfer
bridges disposed on at least one cooling circuit, said heat
transfer bridges being configured to enhance the reverse-flow heat
exchange operation. In some such variations, the cryostat may
include a single cooling circuit equipped with such heat-transfer
bridges.
[0021] In some variations, the cryostat includes a compressor; the
first refrigerant source providing refrigerant to the second
cooling circuit; and the compressor providing refrigerant to the
first cooling circuit. In further variations, the cryostat includes
a second refrigerant source, where the first refrigerant source
provides refrigerant to the first cooling circuit and the second
refrigerant source provides refrigerant to the second cooling
circuit.
[0022] Variations of systems and solutions discussed herein may
pertain to a method of cooling a focal plane array (FPA) disposed
in an integrated detector cooler assembly (IDCA) to an operating
temperature, the method comprising: executing a rapid cooldown
process to bring the FPA down to the desired operating temperature;
and executing a temperature maintenance process to maintain the FPA
at the desired operating temperature.
[0023] In some variations, the rapid cooldown process includes
providing a pressurized gas refrigerant to a high-flow, open-loop
cooling circuit included in a planar, disk-shaped Joule-Thomson
cryostat included in the IDCA. In further variations, the
temperature maintenance process includes providing a pressurized
gas refrigerant to a low-flow cooling circuit included in a planar,
disk-shaped Joule-Thomson cryostat included in the IDCA.
[0024] In some variations, the low-flow cooling circuit is a closed
loop cooling circuit and where the pressurized gas refrigerant
provided to the low-flow cooling circuit is provided by a
compressor included in the IDCA. In further variations, the desired
operating temperature includes a temperature range of 200K to 240K.
In yet further variations, the desired operating temperature may
include a temperature range of 100K to 140K. In further variations
still, the desired operating temperature may include temperatures
between 150K and 200K.
[0025] In some variations, the method further includes stopping
execution of the temperature maintenance process in response to a
de-activation signal provided to the FPA. In further variations,
the method further includes receiving an activation signal
directing the FPA to begin imaging, where said determining is
performed in response to receiving said activation signal.
[0026] In some variations, the method further includes steps of
determining whether the FPA is at the desired operating
temperature; performing said rapid cooldown process in response to
a determination that the FPA is not at the desired operating
temperature; and performing said temperature maintenance process in
response to a determination that the FPA is at the desired
operating temperature
[0027] Variations of systems and solutions discussed herein may
pertain to planar, disk-shaped J-T cryostat, the cryostat
comprising: a cooling circuit configured to operate as a
reverse-flow heat exchanger such that refrigerant entering the
circuit via a refrigerant inlet port is cooled by refrigerant
leaving the circuit via a refrigerant outlet port; a refrigerant
source providing a mixed-gas refrigerant to said cooling circuit;
and heat transfer bridges disposed on said the cryostat along said
cooling circuit, said heat transfer bridges being configured to
enhance the reverse-flow heat exchange operation of the cooling
circuit.
[0028] In some variations, the cooling circuit is equipped with a
gas expander portion disposed in a center of the cryostat, the gas
expander portion being configured to receive high-pressure
refrigerant via the refrigerant inlet port and direct low-pressure
refrigerant to the refrigerant outlet port, such that the gas
expander portion is the coldest portion of the cooling circuit. In
further variations, the heat transfer bridges include polysilicon.
In yet further variations, the heat transfer bridges have a
coefficient of thermal expansion (CTE) that matches the CTE of the
cryostat.
[0029] In some variations, the cryostat further includes a second
cooling circuit configured to operate as a reverse-flow heat
exchange, where the heat transfer bridges are disposed on the
cryostat along said first and second cooling circuits.
[0030] In some variations, the cryostat is formed from two glass
plates, an upper plate and a lower plate. In some such variations,
at least one of the cooling circuits is etched into the lower
plate, the upper plate includes heat transfer bridge pockets to
accommodate said heat transfer bridges therein, and the upper and
lower plates are bonded together to form the cryostat.
[0031] Further scope of applicability of the techniques and
solutions discussed herein will become apparent from the detailed
description given hereinafter. However, it should be understood
that the detailed description and specific examples, while
indicating preferred embodiments of the techniques and solutions
discussed herein, are given by way of illustration only, since
various changes and modifications within the spirit and scope of
the techniques and solutions discussed herein will become apparent
to those skilled in the art from this detailed description.
BRIEF DESCRIPTION OF DRAWINGS
[0032] The techniques and solutions discussed herein will become
more fully understood from the detailed description given herein
below and the accompanying drawings which are given by way of
illustration only, and thus are not limitative of the techniques
and solutions discussed herein, and wherein
[0033] FIG. 1a depicts a variation of an IDCA with two cooling
circuits as disclosed herein;
[0034] FIG. 1b depicts a block diagram of a variation of an IDCA
with two cooling circuits as disclosed herein;
[0035] FIG. 1c depicts a block diagram of a variation of an IDCA
with two cooling circuits as disclosed herein;
[0036] FIG. 1d depicts a block diagram of a variation of an IDCA
with two cooling circuits as disclosed herein;
[0037] FIG. 1e depicts a block diagram of a variation of an IDCA
with two cooling circuits as disclosed herein;
[0038] FIG. 1f depicts a block diagram of a variation of an IDCA
with two cooling circuits as disclosed herein;
[0039] FIG. 2 depicts a variation of an IDCA with two cooling
circuits as disclosed herein;
[0040] FIG. 3a depicts a variation of a planar cryostat having two
cooling circuits as disclosed herein;
[0041] FIG. 3b depicts a variation of a planar cryostat having two
cooling circuits as disclosed herein;
[0042] FIG. 3c depicts a variation of heat exchange operation for a
variation of a planar cryostat having a closed loop cooling circuit
as disclosed herein;
[0043] FIG. 4 depicts a flowchart showing a variation of an
operating scheme for an IDCA with two cooling circuits as disclosed
herein; and
[0044] FIG. 5 depicts a flowchart showing a variation of an
operating scheme for an IDCA with two cooling circuits as disclosed
herein.
[0045] The drawings will be described in detail in the course of
the detailed description of the techniques and solutions discussed
herein.
DETAILED DESCRIPTION
[0046] The following detailed description refers to the
accompanying drawings. The same reference numbers in different
drawings identify the same or similar elements. Also, the following
detailed description does not limit the techniques and solutions
discussed herein. Instead, the scope of the techniques and
solutions discussed herein is defined by the appended claims and
equivalents thereof.
[0047] In view of the foregoing problems, it would be desirable to
have a cooler which can meet the requirements of fast cool-down and
long operation time while remaining small, light-weight, and
relatively low-power. The purpose of this document is to address
this problem and provide a design approach which will meet these
requirements and be small in size, low weight and low input power.
This Design provides a J-T cooler that achieves both performance
requirements and meets size and weight constraints in the same
system; i.e. providing both open and closed cycle modes of
operation in the same IDCA (integrated detector cooler assembly),
and thereby achieves both very fast cooldown and extended steady
state continuous operation without the need for bulky gas
reservoirs or bulky compressors. This Design also provides a method
of operating a J-T cooler to achieve the above-stated
objectives.
[0048] The above problem can be solved by bringing together three
different technologies. The first is the performance of HOT (high
operating temperature) photodetectors such as Infra-Red (IR)
sensors, i.e. operating detectors at temperatures above 77K. The
second is leveraging the high cooling efficiencies of mixed gas
refrigerants at these high sensor operating temperatures. The third
is incorporating the design and operation of planar geometry J-T
cryostats to provide multiple J-T cooling circuits in the same
planar cryostat, a technique not possible in traditional wound tube
heat exchanger J-T cryostat designs.
[0049] An optimal preferred sensor temperature(s) may be selected
for the HOT photodetector(s) in question. In some variations, a
preferred temperature range for a HOT photodetector may be between
100K and 150K. In other variations, a preferred temperature range
may be up to 250K or higher. In some variations, a HOT
photodetector may be an IR detector configured to detect one or
more frequency bands/ranges associated with long-wave, mid-wave,
and short-wave IR.
[0050] Mixed gas refrigerants can then be tailored and, in some
cases, optimized to meet the cooling rates and heat loads of the
high temperature detector(s). The high enthalpy changes achievable
with mixed gas refrigerants compared to traditional refrigerants,
in conjunction with high operating temperatures make very fast
cooldown times achievable. In addition, with mixed gasses, the peak
pressures and flow rates required for efficient refrigeration can
be substantially reduced compared to traditional refrigerants, in
some cases by an order of magnitude or more. This makes possible
the use of relatively small compressors to provide closed-cycle
operation and allows operating in closed-cycle mode with a small
compressor. Planar technology cryostat designs are flexible and
make possible the integration of multiple cooling circuits in the
same refrigeration stage of the Dewar and integrated in an
IDCA.
[0051] In some variations, a fast cooldown loop may be activated to
achieve fast cooldown time to make an MWIR sensor operable quickly,
and then a valve or switching device or assembly (such as the
diverter manifold shown above) may be used to change the cryostat
over into a closed-loop mode that maintains the operating
temperature of the device for an extended period and/or conserves
refrigerant to allow for multiple activation cycles.
[0052] Variations of this concept leverage the advantages of HOT
(high operating temperature) photodetectors such as nBn type MWIR
detectors. Variations of HOT photodetectors may include devices
having reduced dark noise or dark current. Some variations of such
devices may include photo-detectors of the type taught in U.S. Pat.
No. 7,687,871, issued to Shimon Maimon on Mar. 30, 2010, the entire
contents of which are hereby incorporated by reference, and/or
photo-detectors of the type taught in U.S. Patent Publication
2001/0037097 by Jeff Scott, Published on Feb. 17, 2011, the entire
contents of which are hereby incorporated by reference, and/or of
the type taught in U.S. Pat. No. 8,044,435, issued on Oct. 25, 2011
to Jeff Scott, the entire contents of which are hereby incorporated
by reference, and also further variations thereon.
[0053] Mixed gas refrigerants are tailored and optimized to meet
the cooling rates and heat loads of high temperature detectors. The
very high enthalpy changes achievable with mixed gas refrigerants
compared to traditional refrigerants, in conjunction with high
operating temperatures make very fast cooldown times achievable. In
addition, with mixed gasses, the peak pressures and flow rates
required for efficient refrigeration can be substantially reduced
compared to traditional refrigerants; i.e. an order of magnitude
decrease. This makes possible the use of relatively small
compressors to provide closed cycle operation and allows operating
in close cycle mode with a small compressor.
[0054] Planar technology cryostats design are flexible and make
possible the integration of multiple cooling circuits in the same
refrigeration stage of the Dewar and integrated in an IDCA. This
design provides a method of operating a JT cooler to achieve both
performance requirements and meet size and weight constraints in
the same system; i.e. provide both open and closed cycle modes of
operation in the same IDCA and thereby achieves both very fast
cooldown and extended steady state continuous operation without the
need for bulky gas reservoirs or bulky compressors. A variation of
such an IDCA design is shown in FIG. 1a.
[0055] In the variation shown, a gas pressure bottle 1040 may
include a mixed gas refrigerant that includes one or more of
methane, ethane, Argon, isobutene, nitrogen, krypton, propane, and
R14. When a focal plane array (FPA) 1001 or photodetector disposed
on the cryostat 1060 is activated, the diverter manifold 1030 may
be engaged or switched over to open-loop operation such that the
refrigerant from the gas pressure bottle 1040 quickly cools the FPA
1001 through an open loop cooling circuit in the cryostat 1060. In
some variations, an FPA 1001 may reach a desired operating
temperature within ten seconds or less.
[0056] When a desired operating temperature is achieved, the
diverter manifold 1030 may be switched over to a closed-loop
operation, stopping the flow of refrigerant from the gas pressure
bottle 1040 and engages the compressor 1050, which activates to
maintain the FPA 1001 at the desired operating temperature without
a further significant loss of refrigerant. Although not preferred
for quickly cooling an FPA 1001 to a desired operating temperature,
a closed-loop compressor-based 1050 cooling system enables the
cryostat 1060 to maintain the FPA 1001 at the desired operating
temperature for a relatively long period of time. In some cases,
compressor-based cooling can allow for extended ongoing operation
of an infra-red FPA 1001 for up to an hour or longer. In some
cases, the closed-loop cooling circuit can operate indefinitely so
long as there is power to run the compressor 1050. In some such
variation, a closed-loop cooling circuit may also bring the FPA
1001 down to an operating temperature, but such a cooldown process
may take 30 minutes or longer as compared to ten seconds or less
for a high-flow open loop system.
[0057] In some variations, switching to a closed loop operation may
have no effect on the flow of refrigerant from the gas pressure
bottle 1040. In such variations, the FPA 1001 may be meant for a
single-use application or otherwise intended to only be activated
once during the course of a mission or application. In such
variations, the gas pressure bottle 1040 may be reduced in size
such that it holds only enough refrigerant for 10 or 20 seconds of
use in the open loop cooling mode. In some such variations, the
diverter manifold 1030 may include or be replaced with a valve that
controls the flow of refrigerant from the gas pressure bottle 1040.
In further variations, the open loop and closed-loop cooling
circuits may be activated simultaneously or concurrently, such that
the closed-loop cooling circuit begins working to maintain an
operating temperature for the FPA 1001 at the same time that the
open loop cooling circuit begins working to reduce the operating
temperature to the desired level.
[0058] The variation shown has a diverter manifold 1030 with a
charge port. The charge port may accept a high-pressure refrigerant
source or input that can feed a high-flow, open-loop cooling
circuit in the cryostat 1060 and/or can charge a low-pressure
reservoir 1040 that can feed a low-pressure, low-flow open loop
cooling circuit in the cryostat 1060.
[0059] In some variations, where the FPA 1001 is intended for a
single-use application, such as a missile seeker or a targeting
feature of a single-use or limited-use weapon or device, the
diverter 1030 and/or charge port may be omitted. In further
variations, the diverter manifold 1030 may be replaced with a
different type of switch or switching paradigm, such as one or more
valves. In some variations, the open and closed loop circuits may
each have a separate, independently controlled valve to allow for
either or both of the cooling circuits to be closed off at any
time.
[0060] The operating temperature of the FPA 1001, as well as the
selection of open-loop or closed-loop cooling may be controlled by
the CPE (close proximity electronics) board 1020. Variations of CPE
boards 1020 may be custom-made devices or may be programmable
devices that can be configured with a range of operating programs
and parameters. The required logic and programs for control of both
the IDCA and the FPA 1001 disposed in the IDCA may be realized
through the CPE board 1020 included in the IDCA. In some
variations, the FPA 1001 may include or otherwise be attached to a
motherboard also disposed inside the dewar of the IDCA. A connector
may pass from inside the dewar to the CPE board for transmission of
signals between the FPA 1001 and downstream control and image
processing components/systems.
[0061] The variation shown in FIG. 1a includes a cryostat 1060
having dual cooling circuits. The cryostat depicted has one cooling
circuit disposed therein for open-loop cooling, and a second
cooling circuit for closed-loop cooling. Such a variation helps
prevent unwanted refrigerant loss from the closed-loop cooling
system. In some such variations, the closed-loop and open-loop
systems may be simultaneously active for some period while the FPA
1001 is being brought to operating temperature. In some such
variations, the diverter manifold 1030 or cooling system
switch/switches may be configured to allow both cooling systems to
operate simultaneously. Such a variation is depicted in FIG.
1b.
[0062] In the variation shown in FIG. 1b, an FPA 1130 is disposed
in a dewar 1120 on a planar cryostat 1135 having a first 1140 and
second 1160 cooling circuit. Although shown as being adjacent in
the diagram, the cooling circuits 1140, 1160 may be arranged in any
number of configurations, including intertwining/overlapping
configurations. Cooling circuit layouts will be discussed later
with respect to FIGS. 3a and 3b.
[0063] In the variation shown in FIG. 1b, a refrigerant source 1100
feeds the open loop cooling circuit 1140 through a coolant feed
line 1180, 1400 that includes a valve 1150. In some variations, the
valve 1150 may have only two positions--open and closed. In further
variations, the valve 1150 may have a range of positions between
fully open and fully closed. In some variations, the valve 1150 may
include one or more valves and/or manifolds to control or regulate
the flow of refrigerant from the refrigerant source 1100. In some
variations, the refrigerant source 1100 may include a gas pressure
bottle. Some variations of the refrigerant source 1100 may include
replaceable cartridges such as ones similar in size and shape to
commercially available CO.sub.2 cartridges, except filled with
mixed-gas refrigerant as discussed above.
[0064] The open cooling circuit 1140 includes an exhaust vent or
exhaust line 1190, or some combination thereof, that allows the
refrigerant to leave the cooling circuit 1140. In some variations,
the valve 1150 or other flow control device may be disposed on the
exhaust vent/line 1190 instead of the supply line 1180. Such
variations may allow for both the refrigerant source 1100 and the
refrigerant supply line 1180 to be replaced or otherwise
re-configured without altering the operation of the IDCA. In
further variations, the valve 1150 may feed directly into the
cooling circuit 1140 without an intervening supply line 1400. Such
variations may also allow for greater variation in the supply line
1180 arrangement and configuration, making the overall system more
adaptable to a wider range of form factors.
[0065] In the variation shown in FIG. 1b, the second cooling
circuit 1160 is a closed loop cooling circuit 1160 fed by a
compressor 1110. The compressor feeds higher-pressure refrigerant
gas into the cooling circuit 1160 via a supply line 1420 and
recovers lower-pressure refrigerant gas from the cooling circuit
1160 via an exhaust line 1430. In some variations, the supply 1420
and exhaust 1430 lines may feed directly to and from the cooling
circuit 1160. In further variations, one or more valves or switches
1170 may be disposed at ends of or along one or more of the exhaust
1410 and supply 1440 lines between the compressor 1110 and the
cooling circuit 1160. Variations of valve(s) or switch(es) 1170 may
be similar to the type usable with the open-loop refrigerant supply
line 1180. Further variations may include valve(s) 1170 having
flow-regulation capabilities to help maintain desired pressures in
the supply 1440 and/or exhaust 1410 lines.
[0066] In further variations, the closed loop cooling circuit may
be replaced with a low-flow, low pressure open cooling circuit.
Because such a cooling circuit is meant to maintain temperature as
opposed to reduce temperature, refrigerant expenditure in the
low-flow mode may be significantly less than in the high-flow,
temperature reducing mode associated with the high-flow open loop
cooling circuit. In some such variations, the IDCA may be
configured with two coolant sources--one for high-flow temperature
reduction and one for low-flow temperature maintenance. Such a
variation is shown in FIG. 1 c.
[0067] In the variation shown in FIG. 1c, an FPA 1230 is disposed
in a dewar 1220 on a planar cryostat 1235 having a first 1240 and
second 1260 cooling circuit. In the variation shown, the first 1240
and second 1260 cooling circuits are both open loop type cooling
circuits equipped with exhausts 1290, 1510 that allow for the
release/loss of refrigerant gas.
[0068] First 1200 and second 1210 refrigerant sources feeds the
respective open loop cooling circuits 1240, 1260 through coolant
feed lines 1280, 1530 that each include a valve 1250, 1270. In some
variations, one or both valves 1250, 1270 may have only two
positions--open and closed. In further variations, one or both
valves 1250, 1270 may have a range of positions between fully open
and fully closed. In some variations, the valves 1250, 1270 may be
combined into an overall assembly of one or more valves and/or
manifolds to control or regulate the flow of refrigerant from one
or both refrigerant sources 1200, 1210. In some variations, one or
both of the refrigerant sources 1200, 1210 may include a gas
pressure bottle. Some variations of the refrigerant sources 1200,
1210 may include replaceable cartridges such as ones similar in
size and shape to commercially available CO.sub.2 cartridges,
except filled with mixed-gas refrigerant as discussed above.
[0069] Each open cooling circuit 1240, 1260 includes an exhaust
vent or exhaust line 1290, 1510 or some combination thereof, that
allows the refrigerant to leave the cooling circuits. In some
variations, the valves or other flow control devices may be
disposed on the exhaust vent/lines 1290, 1510 instead of the supply
lines 1280, 1530. Such variations may allow for either or both of
the refrigerant sources 1200, 1210 and/or the associated
refrigerant supply lines 1280, 1530 to be replaced or otherwise
re-configured without altering the operation of the IDCA. In
further variations, the valves 1250, 1270 or valve assembly may
feed directly into the cooling circuits 1240, 1260 without
intervening supply lines 1500, 1540. Such variations may also allow
for greater variation in the supply line arrangement and
configuration, making the overall system more adaptable to a wider
range of form factors.
[0070] In the variation shown in FIG. 1c, the first cooling circuit
1240 may be a high-flow open loop cooling circuit meant to provide
rapid temperature decrease. The second cooling circuit 1260 may be
a low-flow open loop cooling circuit meant to provide temperature
maintenance after an initial cooldown. In some such variations, the
first refrigerant source 1200 may be exhausted after between ten
and thirty seconds of use in the high-flow circuit 1240 whereas the
second refrigerant source 1210 may provide anywhere between 30
minutes and several hours of temperature maintenance to keep the
cooled FPA 1230 at a desired operating temperature. In some
variations, the valves 1250, 1270 may be simultaneously triggered
into a fully open state, with no closure or refrigerant flow
stoppage permitted or otherwise intended. Such variations may be
suitable for single-use devices such as cruise missiles. Such
variations may also be suitable for devices having significant
weight or power consumption limitations, or other devices where a
limited usable lifetime or the need to swap out cooling cartridges
is preferable to using/operating a compressor.
[0071] In further variations, the low-flow cooling circuit 1260 may
be configured such that it is equipped with a compressor for
closed-loop operation, but also equipped with valves or switching
devices and a refrigerant source 1210 as a back-up. Such a cooling
circuit may be configured to change from a closed-loop operation to
a low-flow open-loop operation in the event of compressor failure.
Such a solution may allow for an FPA 1230 to remain at operating
temperature for some period of time despite a mechanical
failure.
[0072] In further variations, there may be only a single source of
refrigerant for the IDCA. Such a variation is shown in FIG. 1d. In
the variation shown in FIG. 1d, an FPA 1330 is disposed in a dewar
1320 on a planar cryostat 1335 having a first 1340 and second 1360
cooling circuit. In the variation shown, the first 1340 and second
1360 cooling circuits are both open loop type cooling circuits
equipped with exhausts 1380, 1385 that allow for the release/loss
of refrigerant gas.
[0073] In the variation shown, the supply line 1310 from the
refrigerant source 1300, which may be a gas pressure bottle or a
coolant cartridge or similar device, may feed into a valve 1350 or
manifold or similar switching and/or flow control device. In some
variations, such a coolant cartridge may be configured to be
readily swappable or otherwise replaceable, allowing the
refrigerant source of the IDCA to be recharged periodically.
[0074] In the variation shown, the valve 1350 has two feed lines
leading from it. The first feed line 1370 may be a high-flow feed
line leading to a high-flow open loop cooling circuit 1340 meant to
quickly cool the FPA 1330 down to a desired operating temperature.
The second feed line 1390 may be a low-flow feed line leading to a
low-flow open loop cooling circuit 1360 meant to maintain the FPA
1330 at the desired operating temperature after the initial
cooling.
[0075] In some variations, the valve 1350 may be an integral part
of the IDCA assembly, with the feed lines 1370, 1390 being
internal. In some variations, the valve 1350 may have an off
position, a high flow position, and a low flow position. In the off
position, the valve 1350 prevents any flow of refrigerant from the
source 1300 to the cryostat 1335. In the high flow position, the
valve allow flow from the source 1300 to the high-flow circuit
1340. In some variations, the high flow position may allow flow
from the source 1300 to both the high flow and low flow circuits
1340, 1360. In further variations, the high flow position may allow
flow only to the high flow circuit 1340. In some variations, the
low flow position may allow flow only to the low flow circuit
1360.
[0076] In some variations, once opened, the valve 1350 or switching
assembly/manifold may not be closed. In some such variations, the
valve 1350 may only move from a closed position to a high flow
position and then to a low flow position, where it remains until
all the refrigerant is exhausted or until manually/externally
reset. Such a variation may be useful for detectors in remote
security or surveillance systems where a detector may operate for a
fixed period of time after being triggered into activation.
[0077] Further variations may have a valve or switching device 1350
with a continuous range of motion or more than three discrete
settings. In some variations, such a valve may be controlled by the
process control electronics of the IDCA. In some variations, such a
valve may be fully reclosable during operation, allowing for as
many cooldown and temperature maintenance cycles as can be
accomplished given the available refrigerant.
[0078] In some variations, having a single refrigerant source 1300
may allow for further reductions in form factor and additional
flexibility in arranging a feed line from the source 1300 to the
valve/flow control 1350. In all the variations discussed above,
refrigerant is provided to the cooling circuits in a DC mode. This
allows the refrigerant feed lines to be significantly longer than
those of an AC mode cooling device.
[0079] In other variations, the IDCA may be equipped with a back-up
or secondary refrigerant source. Such a variation is shown in FIG.
1e. In the variation shown in FIG. 1e, an FPA 1730 is disposed in a
dewar 1720 on a planar cryostat 1735 having a first 1740 and second
1760 cooling circuit. In the variation shown, the first 1740
cooling circuit may be a high-flow open-loop type cooling circuit
whereas the second cooling circuit 1760 may be a low-flow
temperature maintenance type cooling circuit. The second cooling
circuit 1760 may be an open loop circuit, a closed loop circuit, or
may be switchable between open and closed loop operating modes.
[0080] In the variation shown, a primary refrigerant source 1700
may supply coolant to either or both cooling circuits 1740 along
coolant feed lines 1750 controlled or regulated by a valve or
diverter 1750. In some variations, the valve 1750 may also control
coolant flow between the primary refrigerant source 1700 and a
secondary refrigerant source 1710. In some variations, if the
primary refrigerant source 1700 is exhausted, inaccessible,
damaged, or otherwise unavailable, the valve 1750 may switch over
to the secondary refrigerant source 1710 to keep the IDCA cooled
and the FPA 1730 at a desired operating temperature.
[0081] In a variation where the primary refrigerant source 1700 is
a compressor supplying refrigerant only to the second cooling
circuit 1760, the secondary refrigerant source 1710 may be a second
compressor or a pressurized gas bottle or cartridge. In the event
the primary compressor 1700 fails or becomes inoperable, the valve
1750 may switch over to the secondary refrigerant source 1710,
which may be another compressor or may be a pressurized refrigerant
source. In a variation where the secondary refrigerant source is a
pressurized refrigerant source 1710, a refrigerant exhaust line
(not shown) that would normally feed refrigerant from the cooling
circuit 1760 back to the compressor may be switched or otherwise
set into an open position such that the exhaust refrigerant is
released into the atmosphere. In some variations, this may also be
accomplished by the valve 1750.
[0082] In other variations, refrigerant for a low-flow circuit of
the IDCA may be captured or recovered from the high-flow
refrigerant source or from exhaust from the high-flow circuit. Such
a variation is shown in FIG. 1f. In the variation shown in FIG. 1f,
an FPA 1830 is disposed in a dewar 1820 on a planar cryostat 1835
having a first 1840 and second 1860 cooling circuit. In the
variation shown, the first 1840 cooling circuit may be a high-flow
open-loop type cooling circuit whereas the second cooling circuit
1860 may be a low-flow temperature maintenance type cooling
circuit. The second cooling circuit 1860 may be an open loop
circuit, a closed loop circuit, or may be switchable between open
and closed loop operating modes.
[0083] The IDCA may be equipped with a first refrigerant source
1800 that is configured to provide refrigerant to the high-flow
cooling circuit 1840. This may be provided by a refrigerant feed
line 1880 which may, in some variations, be equipped with or
otherwise controlled by a valve or manifold or other flow control
device. The high-flow circuit 1840 may also be equipped with a
refrigerant exhaust line 1890 that allows `used` or spent
refrigerant to leave the high-flow cooling circuit 1840. In some
variations, this exhaust line may vent into the surrounding
atmosphere. In other variations, the exhaust line may feed into a
second refrigerant source 1810 either directly or through a valve
1805, such as a check valve, or other flow control device.
[0084] In some variations, the valve 1805 may be configured to
prevent an amount of refrigerant or level of refrigerant pressure
in the second refrigerant source 1810 and its associated cooling
circuit 1860 from reaching or exceeding a certain threshold level.
In such variations, when such a threshold level is reached, the
valve 1805 may cause any additional refrigerant leaving the
high-flow circuit 1840 to be vented into the atmosphere or
otherwise directed to a different destination (such as, for
example, a back-up low-flow/low-pressure refrigerant source [not
shown]).
[0085] The second refrigerant source 1810 may be a compressor that
feeds the low-flow cooling circuit 1860 in a closed-loop mode, so
that refrigerant recovered from the first cooling circuit 1840 is
fed, via a refrigerant feed line 1895, to the low-flow circuit
1860. The refrigerant may then be recovered from the low-flow
cooling circuit 1860 via an exhaust line 1885 that feeds the
refrigerant back into the compressor 1810.
[0086] In another variation, the second refrigerant source 1810 may
be a low-pressure reservoir fed and maintained by the refrigerant
leaving the high-flow circuit 1840. In such a variation, the
refrigerant exhaust line 1885 from the low-flow cooling circuit
1860 may vent into the atmosphere or into a recovery reservoir for
later processing or disposal.
[0087] In yet another variation, refrigerant for the low-flow
refrigerant source 1810 may be acquired directly from the high-flow
refrigerant source 1800 instead of and/or in addition to being
recovered as cooling circuit exhaust 1890. In such variations, the
high-flow cooling circuit may either feed the second refrigerant
source 1810 or vent into the atmosphere. Another feed line (not
shown) may go directly from the first refrigerant source 1800 to
the second refrigerant source 1810. Such a feed line may pass
through a valve or manifold or flow/pressure control device. In
some such variations, the refrigerant source 1800 of the high-flow
cooling circuit 1840 may simultaneously feed 1890 the high-flow
cooling circuit 1840 and provide refrigerant to the second
refrigerant source 1810 for operation of the low-flow cooling
circuit 1860.
[0088] Variations of the solutions described above solve both very
fast cooldowns for missile type applications and provides a means
for operating the IDCA in a continuous closed-cycle mode to support
missions with very long periods of operation. Such a mixed
operation paradigm combines the desirable features of or
technologies currently used separately to solve applications
requirements.
[0089] As can be seen from FIG. 2, variations of such a solution
may be designed with a relatively small form factor. In some
variations, such a two-circuit cooling solution may be designed
small enough for hand-held devices and similar solutions having
limited space and weight requirements (such as, for instance,
aircraft and rocket-propelled devices).
[0090] A variation of a planar cryostat is shown in FIG. 3. In the
variation shown, the cryostat 3001 is a circular disk planar J-T
type cryostat. Further variations may use different cryostat
shapes, such as rectangular or polyhedral shapes and/or non-planar
arrangements.
[0091] In the variation shown, the cryostat has two cooling
circuits, a high-flow, fast cooling circuit 3020 and a low-flow,
temperature maintenance circuit 3010. The high-flow circuit 3020
may be an open-loop cooling circuit equipped with a refrigerant
inlet point 3060 and an exhaust point 3050. The refrigerant rapidly
cools the cryostat by entering the cryostat at the inlet point 3060
and then rapidly passing through the open loop cooling circuit 3020
before being vented to the atmosphere via the exhaust point
3050.
[0092] In the variation shown, the `cold finger` normally extending
from a cryocooler is replaced by the central portion 3090 of the
cryostat. The central portion 3090 is separated into two halves,
which each half being connected to one of the cooling circuits in
the cryostat 3001. Each central portion half 3090 includes baffles
3080 disposed in a chamber meant to take in high-pressure
refrigerant and allow it to quickly expand. The rapid gas expansion
causes the chamber to become a local low-pressure area, which
reduces its temperature. The low-pressure refrigerant then flows to
the exhaust point 3050 along a pathway adjacent to the gas inlet
pathway. This arrangement allows the low pressure refrigerant to
pre-cool incoming high-pressure refrigerant, further enhancing the
effectiveness of the cooling operation. Upon reaching the exhaust
point 3050, the low pressure refrigerant is vented or otherwise
expelled from the cooling circuit in an open-loop
configuration.
[0093] By replacing the `cold finger` with a gas expander 3090 in
the middle of the cryostat, an overall size of the IDCA is further
reduced. Additionally, mechanical complexity is reduced both by
making the IDCA smaller and also by reducing the number of
components included therein. Furthermore, a cryostat 3001 equipped
with a gas expander 3090 cold portion can be operated by providing
DC flow of refrigerant, allow for the refrigerant supply lines to
be longer and more varied in shape. This enables the IDCA and its
associated refrigerant sources/compressors to accommodate a wider
range of form factors. In some variations, a refrigerant source may
be disposed at a significant remove from the IDCA, allowing for
remote operation and temperature maintenance of the detector and
IDCA.
[0094] In the variation shown, the low-flow cooling circuit 3010
may be either a closed loop or an open loop circuit. An open loop
circuit would operate in a manner similar to the high-flow circuit
3020, but with reduced gas flow rates. In the variation shown,
closed-loop cooling operation may be realized by providing
refrigerant into the closed-loop cooling circuit 3010 via the
closed-loop refrigerant entry point 3090. The coolant moves through
the closed-loop circuit, which functions as a reverse-flow
heat-exchanger, introducing high-pressure refrigerant gas that is
then allowed to expand to a lower-temperature in the central
chamber 3090. The lower-pressure gas is then fed back into a
compressor at the closed-loop refrigerant return point 3070.
[0095] In the variation shown, the low-flow cooing circuit also
allows the low pressure refrigerant to flow to the exhaust point
3070 along a pathway adjacent to the gas inlet pathway to pre-cool
the incoming high-pressure refrigerant before it reaches the
expansion chamber 3090, further enhancing the effectiveness of the
cooling operation.
[0096] Some cryostat variations may realize further improvements in
cooling efficiency by further enhancing the pre-cooling portion of
the cooling operation. The variation shown in FIG. 3b realizes such
further enhancement by having heat transfer bridges 3110, 3120
disposed along the high flow and low flow refrigerant circuits in
the cryostat 3100. These bridges may be polysilicon bridges or made
of other materials having high thermal conductivity. Preferably,
such bridges are made of a material having a coefficient of thermal
expansion (CTE) that matches or approaches the CTE of the cryostat
3100. Such bridges 3110, 3120 may have improved heat
transfer/thermal conduction properties, which may be used to
enhance the effectiveness/efficiency of the heat exchanger
operation by enhancing the pre-cooling effect of the outflowing
refrigerant 3150 on the inflowing refrigerant 3140, enabling the
central chamber 3130 to be cooled more effectively. Such heat
transfer bridges 3110, 3120, strapping laterally between the input
3140 and output 3150 lines of a cooling circuit but broken into
sections along the length of the lines, can provide increased heat
exchanger efficiency while maintaining a high thermal impedance
along the length of the lines.
[0097] Such heat transfer bridges may be useful in planar JT
structures for improved efficiency, both in the case of a JT
cryostat 3100 with multiple cooling circuits or a cryostat with a
single cooling circuit. In some variations, a cryostat 3100 may be
equipped with a single cooling circuit equipped with such
heat-transfer bridges 3110, 3120 for improved operating efficiency
of the cooling circuit.
[0098] Variations of a cryostat 3100 may include a planar,
disk-shaped Joule-Thomson cryostat made from two glass plates, with
the cooling circuits being etched into or otherwise created between
the plates. In some such variations, the heat transfer bridges
3110, 3120 may be applied to a top plate of the cryostat at
locations along the cooling circuit(s). In some variations, the
heat transfer bridges 3110, 3120 may be applied to one of the
cryostat 3100 plates before the cooling circuit(s) is/are created
within the cryostat. For polysilicon heat transfer bridges 3110,
3120 used with a glass plate, such bridges may be applied using a
range of techniques suitable for depositing/adhering polysilicon
onto glass. One design uses bridge pockets etched into the upper
glass plate which are filled by sputtering with polysilicon then
chemically and/or mechanically (or chem.-mechanically) polished
flat. The lower glass plate, which may have the cryostat lines
etched into channels, is then bonded to the upper plate to complete
the planar cryostat 3100. Other application techniques may vary
based on the material compositions of the cryostat 3100 and the
heat transfer bridges 3110, 3120. Some variations may use quartz,
ceramics, different types of glass, polyimide or other material
types for the cryostat 3100. Variations may also use materials such
as copper or other thermally conductive materials for heat transfer
bridges 3110, 3120.
[0099] An example of the improvements realized by such pre-cooling
in a closed-loop cooling circuit are shown in FIG. 3c. As can be
seen from the diagram, the gas expander, which is the central
chamber 3130 portion of the cryostat, provides approximately 10K
worth of cooling. By contrast, the heat exchange realized in the
pre-cooling operation can provide approximately 150K worth of
cooling. These ranges are noted only for the sake of example and
are not meant to be limitative on the operation or operating ranges
of the cryostat or cooling circuit(s) therein.
[0100] An example of an activation cycle for an IDCA of the type
described herein is shown in FIG. 4. When a photodetector is
activated for operation 4001, a check may be performed to determine
whether the detector is at a suitable operating temperature 4010.
In some variations, such a check may be performed by measuring a
temperature reading device in the cryostat 3001. Variations of such
a temperature reading device may include a thermocouple or similar
device whose electronic or conductive properties change based on
temperature. Further variations may include a temperature sensor
disposed on the FPA/photodetector that is read by the close
proximity electronics in the IDCA. If the operating temperature is
deemed too high, an open loop cooldown procedure 4020 may be
initiated. Such an open-loop cooldown 4020 may continue until a
desired/required operating temperature is reached. After detecting
or measuring a desired operating temperature 4010, a closed loop
cooling cycle 4030 may be engaged to keep the photodetector at the
desired operating temperature during the rest of the
active/detection period.
[0101] In some variations, a photodetector activation signal 4001
may include a signal indicating a rapid or unexpected detector
activation. Variations of a closed-loop cooling system equipped
with a compressor may bring a photodetector down to a desired
operating temperature without relying on open-loop cooling. Such
closed-loop temperature reduction may take a long time, however. A
level of cooling that can be realized with an open-loop, high-flow
solution in under ten seconds may take up to 30 minutes to achieve
with a closed-loop, low-flow cooling circuit.
[0102] Some variations may have a photodetector configured to
operate primarily with a closed-loop cooling solution. Such
variations, such as certain types of surveillance or monitoring
systems, may have a regular operating schedule of compressor
activation followed by a period of image acquisition, followed by
shutdown. Such a solution may allow for effectively indefinite
operation on such regular intervals so long as there is sufficient
power to operate the compressor and the detector.
[0103] Some variations of such a system may be configured to
automatically commence imaging if certain sensors, such as
proximity or motion sensors, are triggered, or if certain other
environmental conditions are met. A geological monitoring system,
such as a system monitoring a volcano for example, may be
configured to gather a handful of images per day unless a threshold
seismic or temperature event is detected. Such an event may be
treated as a photodetector activation signal 4001. If the
photodetector is not on a regular duty cycle at the time of signal
triggering, it is likely not at the desired operating temperature
4010, and therefore must rapidly be cooled 4020 to commence
imaging. Similar solutions may be realized for weather monitoring
and security systems.
[0104] A variation of an operation cycle for an IDCA of the type
described herein is shown in FIG. 5. In the variation shown, a
signal or other indicator requesting or requiring photodetector
activation 5001 may prompt the IDCA to determine whether the
photodetector is at a suitable operating temperature 5010. Such a
determination may be made by reading a temperature sensor included
the FPA or by reading a temperature sensor included in the
cryostat. If the photodetector is not at a suitable operating
temperature (such as, for example, 77K or less for a traditional IR
photodetector or .about.240K or less for reduced dark current nBn
type photodetectors) 5010, an open loop fast cooldown process 5020
is initiated. Such a fast cooldown 5020 may include releasing a
mixed-gas refrigerant from a cartridge or gas pressure bottle
attached to or switched into a high-flow open loop cooling circuit
connected to the cryostat on which the photodetector is
disposed.
[0105] Once a desired operating temperature is reached, open loop
cooldown 5020 may cease and closed loop cooling operation 5030 may
be utilized to maintain the photodetector at the desired operating
temperature/temperature range for the remaining duration of desired
operation/activity. While the photodetector remains active 5040,
the operating temperature of the detector and/or cryostat is
checked to ensure that a desired operating temperature or
temperature range is maintained. Although indicated as closed loop
operation 5030, such temperature maintenance operation 5030 may
also be realized with a low-flow, open-loop cooling circuit of the
type described above in FIGS. 1c and 1d.
[0106] In some variations, should the operating temperature rise
too far above a desired level, the fast cooldown 5020 operation may
be re-initiated to quickly bring the operating temperature of the
detector back to a desired range/level. In further variations, the
fast cooldown operation 5020 may be engaged and disengaged
independently from the temperature maintenance operation 5030,
allowing the fast cooldown 5020 operation to act as a supplement to
the temperature maintenance operation 5030 if necessary.
[0107] In some further variations, the temperature maintenance
operation 5030 may be suspended or disengaged 5050 when the
photodetector is de-activated or otherwise indicated to stop
imaging. In further variations, excessive cooling of the
photodetector may also be undesirable. In such variations, if the
operating temperature drops below a certain level or range during
operation, the temperature maintenance operation 5030 may be scaled
back, suspended, or ceased altogether 5050 to prevent cooling the
photodetector to an undesirable level. In some such variations,
suspension of cooling during temperature maintenance operation may
5030 be done to reduce power consumption and/or to conserve
refrigerant.
[0108] The techniques and solutions discussed herein being thus
described, it will be obvious that the same may be varied in many
ways. Such variations are not to be regarded as departure from the
spirit and scope of the techniques and solutions discussed herein,
and all such modifications as would be obvious to one skilled in
the art are intended to be included within the scope of the
following claims.
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